In general, a hydraulic excavator as a construction machine largely constituted by an automotive lower traveling structure, an upper revolving structure swingably mounted on the lower traveling structure, and a working mechanism liftably mounted at the front side of the upper revolving structure.
The upper revolving structure is provided with a revolving frame serving as a support structure, a floor member provided on the revolving frame and having an operator's seat mounting section at the rear side for mounting an operator's seat and having a foot rest section at the front side on which an operator rests his or her feet, a cab box provided to cover the periphery and the upper side of the floor member for forming an operator's room on the floor member, and an air conditioner unit provided at the lower surface side of the foot rest section for supplying conditioned air into the operator's room.
The floor member is provided with an internal air inlet port opened inside of the operator's room and an external air inlet port opened outside of the operator's room, and these inlet ports are connected through suction ducts to a suction side of the air conditioner unit. In this case, each duct is formed to have a large passage area, for example, through which air can smoothly circulate (for example, Patent Document 1).